Method of determining manganese in the presence of iron



' Patented May 18, 1943 UNITED STATE-S PATENT OFFICE METHOD OF DETERWINGMANGANESE IN THE PRESENCE OF IRON William D. Brown, Iittsburgh, Pa.

No Drawing. Application September 3, 1941,

- Serial No. 409,429

2 Elaima. (C1. 23-230) ganese content of manganese-rich materials,

which may be high in iron, such as manganese ores, ferro-manganese orthe like, the object of the invention having for a more specific objectthe provision of a method for the volumetric determination of manganesein such materials as have been mentioned above, which method combinesspeed and accuracy.

It is customary in prior methods for determining manganese to oxidizethe manganese to permanganic acid which then is titrated with a standardsolution of ferrous sulphate.

;''Among other objections, the prior methods are rather slow and theamount of manganese that 'can be determined is small, on account of thesmall samples that are required to be used and the rather large volumeof solutions which must be handled before the completion of thedeterminations involved. In accordance with the present invention, alarger sample, of material may be employed, with more accurate results,than has been possible heretofore. I

The process of the present invention is based upon the oxidation ofmanganese by perchloric acid and phosphoric acid, the oxidationresulting in a bright purple solution in which the manganese may bedetermined as described hereinafter. The manganese in this solution ispresent as MnzOs. 7

During this oxidation with perchloric acid, some free chlorine is formedwhich must be removed. In view of the fact that if the aforesaid purplesolution is diluted and boiled for-the removal of chlorine, the solutionis decomposed and rendered unfit for the determination; to avoid this,the chlorine is removed preferably by blowing air through the solutionuntil the air has carried out all free chlorine. Any small trace ofhydrochloric acid is precipitated by silver nitrate.

In carrying out the process the following detailed procedure isemployed.

A sample of 0.5 to 1 gm. is weighed accurately and transferred to a tall300 m1. beaker.

For a term-manganese sample add 10 ml., of

concentrated hydrochloric acid and 35 ml. of

perchloric acid (55%). The resulting mixture is heated to dissolve thesample after which 20 ml.

of phosphoric acid (85%) are added.

For ores, 25 ml. of hydrochloric acid are added and the mixture heateduntil the sample is dissolved, which requires about half an hour. Thenadd ml. of perchloric acid (55%) and 20 ml.

of phosphoric acid.

The resulting solution from either type of material is boiled until thehydrochloric acid is boiled out. The beaker containing the solution thenis heated while covered until perchloric acid fumes condense on thewallsof the covered beaker and run down the sides. In the case offarm-manganese, any carbon should be washed' down by. the fumingperchloric acid, and the heating is continued for about 10' minutes at apreferably-lower temperature on a hot plate, the

perchloric acid still fuming and condensing on v the sides of thebeaker.

The beaker is removed and allowed to cool in the air for /2 minute andthen cooled in water. Add 15 ml. of dilute sulphuric acid (1:-1). Fordriving off the chlorine which is formed, washed air is passed throughthe solution while it .is cooling, which requires about 20 minutes.Then, 10 drops of silver nitrate solution (0.5%) are added, followed byan addition of about 40 ml.

- phate solution. Add 2 ml. of phenanthroline fer- I rous perchlorate asan indicator and titrate with permanganate-to the disappearance of thered color of the indicator. If desired, titration may a be carried tothe permanganate color.

For the titration of ferrous sulphate, add to a beaker ml. of water, 10ml. perchloric acid,

7 ml. phosphoric acid and 10 drops of silver nitrate solution. To thismixture, add 50 ml. po-

tassium permanganate and then 100 ml. ferrous.-

sulphate; After adding the indicator, titrate with potassiumpermanganate to the disappearance of the red color of the indicator.-The potassium permanganate solution of-course has been standardized.

The number of mi. of permanganate used in the test are deducted from thequantity used in the above-described blank. The diiference re-' 5presents manganese. If a factor weight has been used, the readings willequal percentage of manganese.

As has been indicated above, the oxidation product of the manganese isMmOs; i. e., 2 atoms of manganese are combined with one extra oxygenatom which is equivalent to 2 atoms of hydrogen. Since a normal solutionof potassium permanganate contains 54.93 gms. of manganese per liter,the value of the permanganate in this titration per mil. then is 0.05493multiplied by the normality of the potassium permanganate.

If a factor weight is not used the percent of manganese is representedby the mathematical formula:

100 X .6649: X mality at X ml. 0! permanganate Wt. 0! sample For thepreparation of the ferrous sulphate solution, 30 gms. of ferroussulphate (FeSO4HHaO) or 42 gms. of ferrous ammonium sulphate(FeSOMNHOzSOnlZHzO) are wei ed'out and dissolved in 1 liter of watercontaining 35 ml. of perchloric acid (55%) or 50 ml. of sulphuric acid.

I! desired, the final titration may be carried out potentiometrically inaccordance with the usual practice. 7

1. A method of determining manganese in manganese-rich materials, whichcomprises dissolving a weighed sample or the material in hydrochloricacid, removing the hydrochloric acid from the resulting solution,oxidizing the manganese in the solution by perchloric acid in thedrochloric acid,removing the hydrochloric acid from the resultingsolution, oxidizing the manganese in the solution by perchloric acid inthe presence of phosphoric acid, removing free chlorine from theresulting solution by blowing air therethrough, adding to the solutionmeasured volumes of standard ferrous sulphate solution in amountssomewhat in excess of the amount required to react completely with themanganese, and titrating excess ferroussulphate with potassiumpermanganate until the titration-reaches its end point.

WILLIAM D. BROWN.

